Fe₃O₄/graphene composites were synthesized as an advanced electromagnetic wave absorption material by a solvothermal method in a system of ethylene glycol. The Fe₃O₄ nanoparticles were homogeneously anchored on the graphene sheets and the structures of the nanoparticles could be experimentally controlled from ring-like spheres, flower-like spheres to solid spheres by changing the concentration of the oxide graphene. Microwave absorption tests demonstrated that the structures of the nanoparticles had a positive influence on the microwave absorption properties. Especially, for the Fe₃O₄/graphene composite with a flower-like structure, the minimum reflection loss value (RL) could reach −53.2 dB and the bandwidth of RL less than 10 dB (90% absorption) ranged from 8.1 to 16 GHz at a thickness of 2.5 mm, which is among the best-reported performances of Fe₃O₄/graphene materials, showing a huge potential to be used as a candidate for microwave absorbing materials.